Method of forming glass tubing



March 20, 1951 5. J. EVERETT METHOD OF FORMING GLASS TUBING 2 Sheets-Sheet l F/Gl A Hurhuy March 20, 1951 s. J. EVERETTY METHOD OF FORMING GLASS TUBING 2 Sheets-Sheet 2 Filed Feb. 2'7, 1946 Such contraction occurs longitudi 0f the interior of the tube.

Patented Mar. 20, 1951 PATENT ore'rcr;

Mmnon ronmczcuss. TUBING SamuckJflncsEilivmtt,;Thon1ton Heath; England Appltcafgn-Fleliruary 27, race, Serial No. 65mm orevent the tube sticking to the; If

necessary; oxidation of; theoil is p J the. air. from the; inside or by filling: the; tube; with an inert v x-iitrcgenr" The mandrel is provided; 'Iuteiy smooth surface made occurs on to which the thermopIastic to and the mandrel is a of a rna-ii 11ia cnicient of thermal expansion great of the material of the tube. 'as. the tube and mandrel coat the tracts away from the tube andfthe sequently be readily separated from than that tsemi as radially of the tube and it is-fo that oil. which prevents the tube fr'f the mandrel is used. the absen thermoplastic tube is liable ta crac he fractured as a result. of the lon' heemployed but only in'small: am'o as" other wise it interferes with the accurac of the finish':

The never process may he employedln forming tapered or paral lel tubes, anditu s f" circui'ar" or; non ci rcular' cross-section vcr'y long. 0 length of tube is. tozhe treatecfith ndrcrmay. I consistof a plurality of; carefiui-ly senses in greater seen with; is a the- :aiccompanuhag drummer; in when:

f Blfitain'March 12, 1945 e um. (01.. rs-say Figure 1 is an axial section of the apparatus fbr; carrying out the invention accordingvto one method;

Figure 2 is across-section of the pressure casi'ng containing the tube and mandrel, taken: on the'l'ine .II -II'in= Figure 1' Figure" 3 is a side efevati'on partI y in axial section ofa furnace and associated apparatus for carrying out a secondmethod; and

Figure-41 isa diagrammatic side elevation of the complete apparatus used for the said second method".

In the two; examples selected, the tubing treattubingc of fire-resistant glass; such 9. 1 that sold; under the registered trade-mark Pyrex having a coeflici'ent of thermal expansion or 325 x 10- and/the mandles employed are of carhon steel having aconsiderably higher coefiicient efithermal expansion of the order to 10 x 1 0 In Figures 1' and 2; the glass tube I after its left hand end has been sealedi at 2 is fitted on to a: mandrer 3 whiz-this of such a size in crosssection as very nearly to fit the tube I so that there is no risk of the tube I crumpling instead of shrinking when'it is caused to contract onto the mandrel 3L O'i-l i's' then introduced into the time I to prevent the latter stickingto thermalld-rel 3 during the shrinking process.

In; this example; the tube I and mandrel 3- are insertecr in and supported in a cylindrical steel pressure casing 4 which is rendered pressuretight by means of a seal at its open end}. This sear consists of a flanged cap 5' slid-abl fitting over the casing 4 with rubber discs 6 compressed between and the end-of the casing 4 by screws I drawing the fi-ange of the can 5 towards a flange 8- fittd to the casing 4. Thus the discs 6 are; causeeito spread inwardly andgrip the tube Air under pressure is conducted Bottle-casing 4 through a connectingtube- 9 while aircasn be evacuate-(1' from v the tube: If through a connector t ll leading: to a vacuum pump;

The tube is heated in successive sections by the casing 4 being drawn from leftto right in Figure 1 through afurnace N. This: shown as a tubular electrically heated furnace having a 'refiractory liner l l closed: by end walls l3 of as- 3 creased temperature reduces the time necessary to shrink the tube I but increases the risk of the tube I sticking to the mandrel 3.

After the casing 4 has been slowly moved through the furnace I I, it may be allowed to cool to 350 C. and the tube I removed while the mandrel 3 owing to the difference in thermal expansion between the mandreland tube may be easily withdrawn from the tube I.

In Figure 3, the furnace II is of substantially the enclosed portion of the tubing during such heating, whereby said tubing is pressed onto the mandrel, and removing said mandrel from said tubing.

2. In a method of forming a thermoplastic glass tubing having a fine quality internal surface, the steps of placing within a length of preformedrtubing a mandrel of material having a substantially greater coefficient of thermal expansion than the material of the tubing, enclosthe same construction as in Figure 1 except that .zfing at least a substantial portion of the external extensions 20, 2| are secured axially at opposite ends to the walls I3 by screws not shown. It is intended that the glass tube I containing the tained in the furnaces while the tube I and-manc drel 3 so travel, pressure seals of rubber 22 are :area of said tubing, heating said mandrel and tubing to an elevated temperature below the normal working temperature of the tubing and within the range of 650 to 750 C. to cause sofri-i'ng of the tubing and expansion of the mandrel toward the interior surface of the tubing,

applying uniform gas pressure of at least three atmospheres to the exterior of the enclosed pormade to bear on the glass tube at the points of tion of the tubingduring such heatingto. press entry and egit The air pressure is supplied to the interior of the furnace through the connect- .ing pipe 23 from an air pump. An air' admission cock 2 4 and a pressure release cock EFi-are fitted.

In this case, the tube I after it leaves .the furnace 25 II is cooled in the extension 2I which-is; made to serve as a water jacket and-is fitted witha water inlet 26- and water outlet 2T a The tube I ispassed through the hot zone of the furnace II by feeding means at both ends which may operate at the same or different speeds so that the tube I may be kept at -the same weight per foot length during its treatment or may be stretched or compressed. The operating mechanism for the feeding means isshown diagrammatically in Figure 4. It comprises a chuck 28 gripping the tube I at its forward end and a similar chuck 29 gripping the tube before-it enters the furnace II.- The chucks28, 29 are carried on brackets 38 releasably engaging .lead screws SI, 32zjournalledin,the'frame members 33, 34 and prevented from axial movement. These lead screws are rotated'by an electric-motor 35 driving a pulley 36 through a belt 37.- The pulley 36 carries a worm engaging a worm wheel gas may be continuousl passed through it' to prevent oxidation of the oil in the tube--I-;- i

The glass tube I is heated up to about 700-C. in the furnace II in which a pressure of 3. atmospheres upwards is 'maintaineddependingon the thickness of the glass tubeI'.

- By the use of the present inventionf'the glass tube may be providedwith transfers-qr ceramic smarkings on the surface which are thoroughly ,burned in in the furnace and are notremoved by boiling in 'alkalies or acids.

I claim: 1. In a method of forming thermoplastic glass tubing having a fine; quality internal surface, the .stepsof. placing a mandrel within a length. of

preformed-tubing, enclosing at least a substantial :portion of-theexternal area of said tubing. heat:-

ing said mandrel and enclosed tubing to an elevatedtemperature below the normal'working temperature of the tubing and in the range of 650 C. 129150" 6., and applying uniform-gas pressure or; atjea-sti e. atmcsph res'. t0 the; exterior or said tubing onto the mandrel, allowing said'mandrel and tubing to cool substantially .to cause hardening of the tubing and shrinkage of' the mandrel away- -from the interior of the tubing, thereby to facilitate separation of the mandrel and tubing,- and removing said mandrel from aid bi -2.. j l

- '-3..,;In a method o f forming a thermoplastic glass tubing having a jfine quality inte'rnal sureface e ;,;steps, ,or placinga mandrel withing. length of preformed'tubing, enclosing at leasta substantial portionof the exterior surface of said tubing applying uniform gas pressure of at least threeatmospheres to; said space in contact with the-exteriorof said tubing, and passing thereuclosed tubing and mandrel through a heating zone -.to heatthem to an elevated temperature lowerthan the normal working temperature and within the range of, 650 (3. to 750 C. of the tubing,- whereby said tubing is pressed onto themand-rel andxremoving said mandrel from said tubing.

4. Awmethod'according to claim 3, in which said tubing is Withdrawn from said heating zone fasterthan the tubing and mandrel ar fed to the heating; zone,-l thereby drawing said tubing onto said mandrel and reducing the weight per foot of the tubing. I

5. -A method according to claim 1 in which the tubing is heated to about 650 C. andsaid fluid pressure is-exerted by a gas under a pressure of about pounds per square inch.--

A method according to claim 2, including the step of evacuating the interior of said tubing during-the application of heatand pressure. '7. n1ethod .ojfforming glass tubing havingsa. fine quality internal surface, comprising the steps f; enclosing aheating zone, pressurizing said heating zone to agpressure of at least three at- ;m-ospheres while maintaining saidzone at a ter r r 650=750F5 C.,; placing within a length 'of preform edglass tubing a mandrel of a material having a greater coefficient of -thermal-expansion than the glass, passing said tubing and mandrel through said pressurized heating zone tocheat thetubing and mandrel and to exposethe exterior of saidtubing to the pressure in said zonawhereby saidtubing is pressed tightlypnto said-mandrel, permitting said mandrel andtub ing-to cool .after; rer n ov; al' from the heating zone, whereby the difierences in coeflicient of thermal expansion ofsaid mandrel and the tubing cause their'separationfand then removing saidmandrel fromsaidtubing;

: -.3'8..-A method offorming glass tubing having a fine qualit internal surface; comprjsingthe steps 0f enclosing a heating zone, pressurizing said heating zone to a pressure of .at least three atmospheres while maintaining said zone at a temperature of 650-750 C., placing within a length of preformed glass tubing a mandrel of a material having a greater coefficient of thermal expansion than the glass, passing said tubing and mandrel through said pressurized heating zone to heat the tubing and mandrel and to expose the exterior of said tubing to the pressure in said zone whereby said tubing is pressed onto said mandrel, passing said mandrel and tubing through an enclosed cooling liquid, and then removing said mandrel from said tubing.

SAMUEL JAMES EVERETT.

The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,301,714 Keuppers Apr. 22, 1919 1,583,464 Housekeeper May 4, 1926 2,084,811 Keen June 22, 1937 2,286,401 Everett June 16, 1942 2,373,816 De Roche et al. Apr. 17, 1945 2,393,979 Everett Feb. 5, 1946 2,426,341 Canfleld Aug. 26, 1947 

